My contributions:

Requirements

Introduction I gathered a lot of information and then I started to migrate the component of the new Joomla 2.5 to 3.0 (still in beta1). Below is some important information used for migration:

Use "display_errors On" to help in errors debug.

Migrating Joomla 2.5 to Joomla 3.0:

Remember that you need to add Legacy any place you are directly extending JModel, JView or JController. If it is indirect (like through JModellist) you don't have to, it's already taken care of. Other than that and the fact that as announced long ago deprecated code has been removed (I'd guess that JParameter is the biggest impact ) extensions should only need minor changes ... although you will want to look at the output changes that Kyle is working on. Of course if you are building stand alone platform applications the new MVC and jApplicationWeb/JApplicationCLI are completely the way you should work and the nice thing about the way we have done this is that the new packages are already right there on your server having arrived with the CMS. (Elin in development list)

Samples:

DS

Since we've removed the DS constant in 3.0, we need to replace the uses of the constant in com_media. The most unobtrusive change is to simply replace it with PHP's DIRECTORY_SEPARATOR constant since DS is an alias to that.